This invention relates to a drive wheel the diameter of which can be continuously changed as it pulls a chain. It also relates to a transmission employing that drive wheel, where the ratio of output rpm to input rpm can change continuously.
Most engines operate at maximum efficiency at a particular rotational speed (rpm, revolutions per minute). At slower or faster speeds, they are less efficient and suffer excessive heat or wear. For that reason, it is desirable to have an engine operate at its peak efficiency rpm and use a transmission to obtain the desired rpm.
In a typical transmission, the engine drives a number of gears of different diameters and the output power is taken off the engine by using different combinations of those gears. Alternatively, sprocket wheels connected by a chain can be used instead of gears. Thus, to change the output to input rpm ratio it is necessary to disengage a gear and engage a different gear or shift a chain from a sprocket wheel of one diameter to a sprocket wheel of a different diameter.
That type of transmission has a number of deficiencies. First, during the time required to shift gears, no power is being drawn from the engine. This power gap is responsible for the forward-backward jerks that passengers in cars and trucks feel when the gears are shifted.
Second, the ratio of input rpm to output rpm must be a rational number (i.e., a number that can be expressed as the ratio of two integers). This ratio is the number of teeth on the input gear or sprocket wheel divided by the number of teeth on the output gear or sprocket wheel, and that ratio is necessarily a rational number as an integer number of evenly-spaced teeth must be used. If the desired ratio is irrational, such as √2, for example, it cannot be obtained using gears or sprocket wheels.
Third, only certain a limited number of ratios can be selected. In a car, there may be only 3 or 4 possible ratios. This means that if the ratio of peak efficiency is not one of the possible ratios, say it is 1.616, for example, the engine never operates at peak efficiency.